Work on the purification and characterization of the mitochondrial hydroxyacid-oxoacid transhydrogenase which catalyzes the alpha- ketoglutarate dependent oxidation of gamma-hydroxybutyrate (GHB) to succinic semialdehyde will continue. This enzyme which has been found in the soluble fraction of the mitochondria from brain, kidney and liver has already been partially purified. These studies will be of interest since this is the first report of a hydroxyacid-oxoacid transhydrogenase in mammalian tissue. A developmental study of the mitochondrial transhydrogenase and the cytosolic NADP+ oxido-reductase (GHB dehydrogenase) in brain and kidney has been completed. Since these two enzymes, one mitochondrial and the other cytosolic, are responsible for the catalyzing the initial rate-limiting step in the catabolic pathway for the neuroactive compound, GHB, this study will aid in our understanding of how tissue concentrations of this compound are regulated in the fetus, the newborn and from birth to adulthood. This work has been completed and has now been published (Nelson and Kaufman, Developmental Neuroscience 1994). A new aspect of this work is the examination of human fibroblasts for the transhydrogenase activity. Work on the effects of the neuroactive compound, GHB, at the cellular level has been temporarily discontinued since the position of the investigator who was carrying out these studies has been terminated. Work on the purification and characterization of enzymes in the oxidative pathway for GHB has also been affected by the loss of this investigator.